Basic Motor Technology
- Brushless DC motors (BLDC motors) create movement using a three-phase AC (alternating current) field coil.
- ⚙️ These motors look like DC (direct current) motors, but work like synchronous motors.
- A rotating magnetic field pulls the rotor using magnets.
- BLDC motors need constant voltage from the VFD (variable frequency drive), even when not spinning.
- ⚡ They appear in machine tools, servo systems, compressors, conveyor belts, and metering pumps.
- Synchronous reluctance motors (SyncRM motors) use the same shape as asynchronous ones.
- ⚙️ Inside, their rotors avoid magnets and use soft magnetic materials.
- This motor waits for the rotation field before starting.
- ⚡ SyncRM motors go in turbines, fans, mixers, compressors, centrifuges and pumps.
- SyncRM motors match IE4 (International Efficiency 4) standards for energy use.
Motor Efficiency
- Asynchronous motors follow IE (International Efficiency) classes: IE1, IE2, IE3, IE4.
- ⭐ IE1 means standard efficiency, IE4 means super premium efficiency.
- Efficiency rises as power (kW) increases.
- ⚡ Motors under 0.12 kW also need minimum IE2 class.
- Since July 2023, motors between 75 kW and 200 kW must meet IE4.
Motor Starting Methods
- Direct-on-line start (DOL) applies full voltage instantly.
- ⚙️ This creates high current and thermal stress.
- DOL is okay when motor current is under limits.
- ⚡ Motors above 4 kW may need star-delta instead.
- Star-delta starter begins with lower voltage.
- ⚙️ Then it switches to full voltage in delta mode.
- Useful for fans, pumps, and other load-growing systems.
- ⚡ Needs precise timing relays and good phase sequence.
- Soft starters control the voltage rise smoothly.
- ⚙️ They help avoid mechanical shock and limit high torque.
- Good for frequent starts, presses, elevators, or HVAC systems.
- ⚡ Soft starters allow adjustable start and stop times.
- Variable Frequency Drives (VFDs) allow stepless speed control.
- ⚙️ VFDs change frequency and voltage together.
- They let motors operate efficiently across all speeds.
- ⚡ Ideal for pumps, fans, process machines.
Startup Characteristics
- Startup current (IA) can be 4–8 times the normal.
- ⚙️ Starting torque varies by method: DOL > star-delta > soft start > VFD.
- ⚡ Slip speed = (synchronous speed – actual speed)/synchronous speed.
Efficient Motor Starting Currents
- IE3 and IE4 motors use better materials.
- ⚙️ They have lower copper losses and higher inductance.
- This leads to higher starting currents.
- ⚡ Tripping systems must tell apart inrush from fault.
Motor Protection
- Overload relays protect motors from overheating.
- ⚙️ Use manual reset for safety, or auto reset for automation.
- Special setups like star-delta may change how relays behave.
- ⚡ Correct relay setting = rated current.
- Back-up fuses protect from short circuits.
- ⚙️ They must match relay specs.
- Motor protection devices include bimetal, thermistor, and CT-based relays.
- ⚡ CT-based (current transformer) relays like ZW7 work well for big motors.
- Heavy duty starts need longer trip times.
- ⚙️ Otherwise, relays trip too soon and kill protection.
- Bridging motor protection can skip protection during start.
- ⚡ Only okay for small motors with low start current.
- Capacitor compensation helps reduce reactive current.
- ⚙️ When capacitors sit near the motor, set the relay to real motor current.
- ⚡ This keeps cables cool and efficient.
- Thermistors react to temperature.
- ⚙️ PTC (positive temperature coefficient) rise fast with heat.
- Stator-critical motors need quick response in windings.
- ⚡ Rotor-critical motors (like >15kW) may overheat inside without warning.
Wiring and Circuit Diagrams
- Circuit diagrams show how electricity flows.
- ⚙️ They come in block, detailed, and equivalent formats.
- Wiring diagrams show physical connections.
- ⚡ There are also unit, interconnection, and terminal diagrams.
- Contactor markings follow EN 81346-2.
- ⚙️ Letters (like Q) and numbers show what each contactor does.
- ⚡ Combinations (e.g., reversing star-delta) keep base types.
This is the full picture of motor technology and protection from the Eaton Wiring Manual 10/23, organized simply for learning. Whether you’re starting motors or protecting them, now you understand the essentials.
My Diary - Leonardo Cardillo 